I'm not sure if this is an intentional feature or not, so I'm hesitant to post it in the bugs.
When you switch tabs in Firefox (or when I do), everything stops, even if it's the AI's turn. The game only progresses when I'm on the tab. Is this intentional? The only annoying part is when the opponent has about 20 creatures and I lay a SoSa and just want to sit back, multitab, and come back afterward.